The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Reverse osmosis systems use a membrane to separate a stream of liquid (feed) containing dissolved solids into two streams. The first stream is a pure liquid that is formed by passing fluid through the membrane of the reverse osmosis system. A second stream of liquid also leaves the membrane housing 12 and has a higher concentration of dissolved solids, which is referred to as brine or reject.
Before reaching the membrane housing 12, the liquid, such as sea water, has been filtered so that large suspended particles have been removed. It has been found that by recirculating a portion of the brine with and incoming feed to the membrane, the amount of permeate to be extracted from a given volume of feed membrane performance can be increased. Providing the brine to the feed input is referred to as “brine recirculation”. Typically, the pressure differential between the feed and the brine is relatively small (about 1 bar to 3 bar).
Systems that operate at very high pressures (exceeding 100 bar) often require brine recirculation. Consequently, the equipment used in such systems must be designed for accommodating such pressures. Typically, to accommodate high pressures, the rating of the pump must be suitable to accommodate the pressures. Also, the shaft seals for high pressure pumps are prone to frequent failures. Special motors must also be provided to handle high thrust loads generated by the high working pressure. Such systems are also prone to premature bearing failure. Variable frequency drives are also required for driving the external motors to allow variations in the flow rates. All of these features add to the expense and complexity of the reverse osmosis system.
Referring now to FIG. 1, a reverse osmosis system 10 according to the prior art is set forth. The reverse osmosis system 10 has a reverse osmosis membrane housing 12 that has a membrane 14 disposed therein. The membrane housing 12 has a feed fluid input 12A, a brine fluid outlet 12B, and a permeate outlet 12C. As briefly mentioned above, feed fluid enters the feed fluid input 12A and, with the membrane 14, divides the fluid into a permeate stream exiting the membrane housing 12 at the permeate outlet 12C and a brine stream at the brine outlet 12B. Feed fluid is provided to the feed fluid inlet 12A through a high pressure pump 16. A valve 18 may be used to regulate the feed pressure in the flow rate.
The brine outlet 12B and the brine therein may be controlled by a valve 22. The depressurized brine is disposed in a drain 20.
Referring now to FIG. 2, a recirculation pump 30 may be disposed in a recirculation pipe 32 so that a portion of the brine exiting through the brine outlet 12B is communicated to the feed fluid inlet 12A. A combination of the recirculated brine and the brine from the feed pump 16 enter the feed fluid inlet 12A of the membrane housing 12.
Referring now to FIG. 3, the reverse osmosis system may also include a turbocharger 40 coupled to the brine outlet 12B by a pipe 42. In particular, the turbocharger 40 includes a turbine portion 40T and a pump portion 40P. The turbine portion 40T receives brine through the pipe 42 through a valve 46. The valve 46 provides flow and pressure regulation. The valve 46 and the turbine portion 40T receive the brine fluid, which operatively turns the turbine within the turbine portion 40T and thus provides a rotating force to the pump 40P. Feed fluid from the high pressure pump 16 and the valve 18 is received in the pump portion 40P. The pressure is increased to a level needed for the membrane 14 for optimal operation. The pressurized feed fluid that has been pressurized by the pump 16 and the pump portion 40P is received within the feed fluid inlet 40A. The purpose of the turbocharger 40 is to reduce the discharge pressure of the high pressure pump 16 to reduce energy. A pump with a lower pressure rating is also less costly. The shaft 48 between a motor 50 and the turbine portion 40T must include a shaft seal. The shaft penetrating the housing of the turbocharger 40 may be a source of potential shaft leakage regardless of the operating pressure. The motor 50 is driven by a variable frequency drive 52.